Mobile communication devices have become increasingly common in current society for providing wireless communication services. The prevalence of these mobile communication devices is driven in part by the many functions that are now enabled on such devices. Increased processing capabilities in such devices means that mobile communication devices have evolved from being pure communication tools into sophisticated mobile multimedia centers that enable enhanced user experiences.
A mobile communication device may operate in a dual connect (DC) mode, in which the mobile communication device is configured to transmit/receive two signals simultaneously in a pair of transmit/receive bands. In a non-limiting example, the mobile communication device can be configured to operate in the DC mode to transmit/receive two signals in fifth-generation new radio (5G-NR) bands 77 and 79, respectively. The 5G-NR band 77 ranges from 3.3 GHz to 4.2 GHz and the 5G-NR band 79 ranges from 4.4 GHz to 5.0 GHz. A narrow transition band ranging from 4.2 GHz to 4.4 GHz separates the 5G-NR band 77 and the 5G-NR band 79.
Fractional bandwidth, which is often quoted as a percentage, is a commonly used measure for comparing bandwidths between signals. The fraction bandwidth, which may be expressed by a percentage, is defined as (f2−f1)/fc, wherein f1, f2, and fc represent lower frequency, upper frequency, and center frequency of a signal, respectively. Accordingly, the fractional bandwidths of the 5G-NR band 77 and the 5G-NR band 79 can be 24% and 12.9% respectively. In this regard, the 5G-NR band 77 has a wider bandwidth than the 5G-NR band 79.
The mobile communication device may be configured to transmit/receive the two signals in the 5G-NR bands 77 and 79 via a common antenna port. In this regard, a diplexer circuit(s) is often required to separate the two signals presented at the common antenna and to route the separated signals to appropriate receivers. A conventional low-temperature-cofired-ceramic (LTCC) diplexer can function well with very wide fractional bandwidth, but requires a wider transition band. In contrast, an acoustic diplexer can function well with a narrower transition band, but has problems handling wider fractional bandwidth. In this regard, it may be desirable to have a diplexer circuit that can function with wider fractional bandwidth and a narrower transition band.